4784
With 11 on hand we proposed to take advantage of be formed by standard methods without undue diffithe stereospecificity of the glycol monotosylate rearculty. rangement to form the desired product 2. The stereoWe are examining the reaction of the ketone 2, the specificity of such rearrangements has been well estabalcohols 3 and 4, and the derivatives of 3 and 4 to deterlished in the synthesis of many bicyclic ~ y s t e m s ~ ~ - *mine ~ the reactivity of trans-bicyclo[4.1 .O]heptanes. including trans-bicyclo[7.1 .O]decan-2-one. The most We have also synthesized by similar methods cis- and important feature for our choice was that the rearrangetrans-bicyclo[5.1.O]octanes and cis- and trans-bicycloment could be run under very mild conditions.1’z2 [6.1 .O]nonanes and are examining their reactivity toThus, treatment of 11 with tosyl chloride in pyridine ward a variety of reagents. and rearrangement of the monotosylate 14 with 1 Joseph V. Paukstelis,* Jar-lin Kao equiv of potassium tert-butoxide in THF for 10 min gave Department of Chemistry, Kansas State Uniaersity a product in 83 yield which we assigned as 2. MolecuManhattan, Kansas 66506 lar distillation gave a pure product which exhibited Receiaed April 18, 1972 v”,”,‘: 3010’and 1703 cm-I and 6 (CCL) $0.4 ppm (1 H, m, cyclopropyl and no resonances below 2.5 ppm).18 When the reaction was allowed to proceed for 19 hr and New Anionic Rearrangements. XVI. 1,2-Anionic with 2 equiv of potassium tert-butoxide, a different prodRearrangement from Sulfur to Carbon in uct was isolated in 7 3 z yield. This product, 15, was Ben~ylthiotrimethylsilane’-~ identical in all respects with cis-bicyclo[4.1 .O]heptan-2Sir: one prepared by a known route: * j vzy: 1690 cm-I and 6 (CC1,) 1.O ppm (highest field multiplet). The isolation Many organic ethers may be converted to isomeric of 15 is consistent with the initial formation of2 followed alcohols in the presence of excess organolithium reagent by isomerization to 15. When the rearrangement was by the classical Wittig rearrangement. The analogous rearrangement of organic sulfides to mercaptans has not previously been 0bserved.j Generally, metalation of the rather acidic proton a t9 sulfur in sulfides,6 sulfoxides, lo and sulfones produces stable carbanions which do not rearrange. -H -H 14 We now find that benzylthiotrimethylsilane (1) re2 15 l 4 to a-trimethylarranges rapidly and in high run in tert-butyl alcohol-d the product contained less than silylbenzylmercaptan (2) in the presence of excess tert33 mol deuteriumz6indicating that the rearrangement butyllithium. This is apparently the first example proceeds primarily without enolization of any kind. If the rearrangement of 14 is done in the presence ( 1 ) Previous paper in this series: R . West and P. Boudjouk, J . Amer. Chem. SOC.,in press. of a reducing agent, such as potassium tri-tert-butoxy(2) For a review of silylanionic rearrangements see R . West, Pure aluminum hydride, the ketone 2 can be reduced to a Appl. Chem., 19,291 (1969). mixture of alcohols 3 and 4 in a ratio of 2 : 1, respec(3) Research sponsored by Air Force Office of Scientific Research (SRC)-O.A.R., USAF, Grant No. AF-AFOSR 70-1904. tively. Comparison of the nmr and infrared spectra (4) (a) G . Wittig and L. Lohmann, Justus Liebigs Ann. Chem., 550, of 3 and 4 and the known cis-bicyclo[4.1 .O]heptan-cis260 (1942); (b) D. L. Dalrymple, T. L. Kruger, and W. N. White in “The Chemistry of the Ether Linkage,” S. Patai, Ed., Interscience, New and -trans-2-0ls*~(16 and 17) indicated that the com-
z
z
16
17
pounds were not the same. The presence of the complex multiplets in the nmr spectrum of 3 at 6 (CCIq) -0.5 ppm and for 4 at 0.2 ppm clearly indicated the presence of cyclopropyl in 3 and 4. On the basis of the chemical shifts of 16 and 17 and the possible conformations for 3 and 4 one can tentatively assign the structure of the two alcohols as trans-bicyclo[4.1 .O]heptan-trans-2-01 for 3 and trans-bicyclo[4.1 .O]heptancis-2-01 for 4.14 The alcohols are not stable to glpc but can be purified by trap-to-trap distillation (54 yield). Acetates and other derivatives of 3 and 4 can
z
(22) G. Buchi, W. Hofheiz, and J. V. Paukstelis, J. Amer. Chem. Soc., 91, 6473 (1969). (23) M. Nussim and Y. Mazur, Tetrahedron, 24, 5337 (1968), and references therein. (24) D. Redmore and C. D. Gutsche, Adoan. Alicycl. Chem., 3, 1 (1971), and references therein. (25) W. G. Dauben and G. H. Berezin, J. Amer. Chem. Soc., 85, 468 (1963). (26) The mass spectral analysis indicated 67% 0 - d , 17% 1-d, 14% 2-d, and 2 % 3-d.
Journal of the
American Chemical Society
94:13
York, N. Y . , 1967, p 617; (c) U. Schollkopf, Angew. Chem., Int. Ed. Engl., 9, 763 (1970). (5) A Wittig-like mechanism has been used to explain the formation of stilbene from benzyl sulfide and strong base. See T. J. Wallace, H . Pobiner, J. E. Hofmann, and A. Schriesheim, J . Chem. Soc., 1271 ( 1965). (6) For example: CHaSCHzLi;’ PhSCH:Li;S lithiated 1,3-dithianes.9 ~. (7) D. J. Peterson, J . Org. Chem., 32, 1717 (1967). (8) H. Gilman and F. J. Webb, J. Amer. Chem. Soc., 71,4062 (1949). (9) E. J. Corey and D. Seebach, Angew. Chem., Int. Ed. Engl., 4, 1075 (1965). (10) E. J. Corey and M. Chaykovsky, J . Amer. Chem. Soc., 87, 1345 (1965). (11) B. S. Thyagarajan, Mech. React. Sulfur Compounds, 4, 115 (1969). (12) Recently we reported the almost quantitative Wittig-type rearrangement of triethylbenzyloxysilane to phenyltriethylsilylcarbinol in the presence of excess t e r t - b ~ t y l l i t h i u m . ~ ~ (13) R. West, R . Lowe, H . F. Stewart, and A. Wright, J . Amer. Chem. Soc., 93,282 (1971). (14) The migratory aptitude of silicon in 1,2 anionic rearrangements is remarkable.*,13 When carbon migrates, as in the Wittig rearrangement, a simple 1,2 sigmatropic suprafacial shift is disallowed by the Woodward-Hoffmann rules4oo.15with the result that rearrangements proceed slowly, often in low yield, and apparently by a cleavage-recombination mechanism. Silicon probably migrates cia a pentacoordinate transition state without the above symmetry restriction^.^^ (15) R. B. Woodward and R. Hoffmann, “The Conservation of Orbital Symmetry,” Academic Press, New York, N. Y., 1970. (16) A. G. Brook, G . E. LeGrow, and D. M. MacRae, Can.J . Chem., 45, 239 (1967). ( 1 7) The remote rearrangement LiCsH4SSiMea MeasiC~HaSLi has been reoorted: see A. R . Bassindale and D. R . M. Walton, J . Organometai. Chem., 25, 389 (1970).
1 June 28, 1972
. )
4785 of a Wittig-type rearrangement involving migration from sulfur to negatively charged carbon. 2 undergoes quantitative rearrangement back to 1 in the presence of a radical catalyst, or upon heating, but not in the presence of catalytic amounts of base. In these respects 2 differs sharply from phenyltrimethylsilylcarbinol (4) which rearranges to the alkoxysilane 3 thermally only in poor yield and at high temperature, but undergoes the rapid Brook rearrangement'6 to 3 in the presence of catalytic quantities of base. catalyzed rearrangements
PhCHsYSiMet-
4
A
1,Y=S 3,Y=O t-BuLi > 1 equiv
PhCHYSiMe,
v
Products from Derivatization of Anion of 1,
__-_ HzO ,
~
7
H
0
0
PhCHRSSiMe, PhCH(SiMe3)SR PhCH(SiMe2CHzR)SR PhCHSR
--.
Trapping agent--CH3I MezSOa EtsSiCl _ _R =_ CHI CH3 Et3Si
89.9 9.7 0.4
0 94.3 4.1 1.6
93.2 6.7 0.1
0 90.4 9.6 0
s ~ M ~ ~ tions occurs rapidly in 95% yield at -78", 79% at Ph/.HYH 0", l 9 with the interesting difference that the alkylating 2,Y=S 4,Y=O
anionio rearrangements n
Table I.
SiMea
I
PhCHY-
1, bp 130" (14 Torr), ~ * O D 1.5305, was prepared in 86 % yield by silylating benzylmercaptan with excess hexamethyldisilazane in refluxing toluene. tert-Butyllithium (0.33 mol; 1.24 M in pentane) was added to 59.0 g (0.30 mol) of 1 in 266 ml of dry tetrahydrofuran at -78". A homogeneous solution resulted, showing in its pmr spectrum only one trimethylsilyl resonance and the removal of one benzylic proton. A peak at T 12.15, corresponding to the SiCH2Li moiety, l8 indicated 10 % metalation of the trimethylsilyl group (uide infra). The anion solution was warmed to -22" and 150 ml of 2.2 M aqueous MgCL was injected into the agitated solution. The mixture was warmed to 25", the organic layer separated from the aqueous layer, and solvent evaporated. Vacuum distillation yielded 53 g of a clear oil which contained 0 . 4 z PhCH2SH and 9 9 . 6 x 2. 2 was obtained almost quantitatively even if the anion, once formed, was heated to 180" followed by protonation at 100". Structure 2 was assigned from the proton nmr (CCl,, C,HI2) which showed a singlet at T 9.96 (SiMe3), a doublet at 8.38 (SH), a doublet at 6.73 (CH), and a singlet at 2.86 (C6Hj), with relative intensities 9.0 : 1.O : 1.0:5.2. The ir spectrum (neat) shows a weak SH stretch at 2570 cm-I. The rearrangement was repeated with the anionic species being trapped in turn with methyl iodide, dimethyl sulfate, and triethylchlorosilane by injecting the derivatizing agent into samples of anion at - 78 ". The resulting solutions were evaporated of solvent, totally distilled under vacuum, and separated into individual compounds by preparative glc. That both methylations occurred only at sulfur rather than at the carbon is proven unequivocally by the nmr which shows a single methyl resonance at 7 8.15 in the isolated product. Silylation also occurred at sulfur since acid hydrolysis of this product gave only hexaethyldisiloxane and 2. Minor products arise from cleavage of 1 by tert-butyllithium and trapping of PhCH(SiMezCHzLi)SLi, the species responsible for the high-field resonance in the anion nmr. No 1 was recovered, even when methyl iodide injection followed tert-butyllithium addition by as little as 10 sec (see Table I). The rearrangement of 3 to 4 under the above condi(18) G. E. Hartwell and T. L. Brown, J . Amer. Chem. SOC.,88, 4625 (1966).
derivatizing agents trap metalated 3 predominantly in the unrearranged form as PhCHMeOSiMe3. Pitt has reported the radical-catalyzed quantitative 1,2 migration of the trimethylsilyl group from silicon to sulfur in (Me3Si)2Si(SH)Me.20 We now report the first example of a radical-catalyzed 1,2 migration of a trimethylsilyl group from carbon to sulfur. Thus 250 mg of 2 heated to 100" in heptane in the presence of 17 mg of azobisisobutyronitrile yielded 92% 1 and 8 % recovered 2 after 37 min. Negligible rearrangement of 2 to 1 occurred in the absence of the radical initiator, or in the presence of the nonradical products of previously decomposed initiator. Heating 2 to 195" neat for 30 min gave quantitative first-order thermal rearrangement to 1, k = 0.97 X sec-I. In contrast, 4 rearranged to 3 only at 275" and then slowly with formation of several side products. However, 4 does undergo the silyl anti-Wittig rearrangement l 5 in tetrahydrofuran-pentane solution to give 3 in 85-90z yield, when treated 3 min with 0.085 equiv of liquid sodium-potassium alloy at 0", or when treated 25 hr with 0.10 equiv of n-butyllithium at 25". The alloy is not observed to be consumed nor is hydrogen evolved. 1 and 3 are thus clearly the thermodynamically favored products, formed when the neutral species are equilibrated. Curiously 2 does not rearrange to 1, nor 1 to 2, either in the presence of sodium-potassium alloy or under any other conditions commonly used in the catalytic silyl anti-Wittig rearrangement. Sodium-potassium alloy rapidly liberates hydrogen from 2. The thermal rearrangement of 2 to 1 is accelerated only slightly at 195" in the presence of small amounts of base. The 1,2 sulfur-carbon silylanionic rearrangement should have considerable synthetic utility in generating carbon-functional organosilanes as exemplified by the rearrangement of sulfide 5 to mercaptan 6 . 1. t-BuLi
CHaSSiMez-t-Bu 5
*=
t-BuMezSiCHzSH 6
5 treated with excess tert-butyllithium in 1 : 1 tetra-
hydrofuran-pentane solution for 16 hr at -45", followed by aqueous protonation, yielded 6 , 35%, and recovered 5, 6 5 x . 6 was isolated by preparative glc and identified by 100-MHz pmr and mass spectrosCOPY * (19) R. West and A. Wright, unpublished results. (20) C. G . Pitt and M. S. Fowler, J . Amer. Chem. SOC.,90, 1928 (1968).
Antony Wright, Daniel Ling, Philip Boudjouk, Robert West* Department of Chemistry, Unicersity of Wisconsin Madison, Wiscotisiii 53706 Recerced April 6, 1972
Communications to the Editor
